fix(5.0): missing not nil constraint (#76)

Author: YoRyan

core/5.0/global.d.ts

@@ -102,7 +102,7 @@ declare function next(table: object, index?: any): LuaMultiReturn<[any, any] | [
  * See function next for the caveats of modifying the table during its
  * traversal.
  */
-declare function pairs<TKey, TValue>(
+declare function pairs<TKey extends AnyNotNil, TValue>(
     t: LuaTable<TKey, TValue>
 ): LuaIterable<LuaMultiReturn<[TKey, NonNullable<TValue>]>>;
 declare function pairs<T>(t: T): LuaIterable<LuaMultiReturn<[keyof T, NonNullable<T[keyof T]>]>>;